Multilayer, coextruded blown film is used in flexible packaging applications. Typical films include multiple layers formed from different polymers, such as one or more of a polyamide layer, a polyethylene layer, a layer formed from ethylene vinyl alcohol (EVOH) as an oxygen barrier, a layer formed from polyolefins for moisture resistance, and/or one or more tie layers, such as layers formed from anhydride modified ethylene acrylate resins and maleic anhydride grafted polyethylene.
Polyamides, such as polyamide 6 (PA6) may be included in typical films, providing good barrier properties and mechanical strength. However, the relatively high crystallization rate of PA 6 can limit the processing window and cause problems such as curling in unsymmetrical film structures.
Commercially available copolymers of polyamide 6 and polyamide 6,66 (PA 6/66) such as Ultramid C40 from BASF typically have lower melting points and correspondingly lower crystallization rates. For some blown film processes, it may be desirable to have slightly higher melting points and low crystallization rates, or very low crystallization rates with higher melting points.
Some coextruded blown film processes employ blends of PA6 with a polyamide 6/66 copolymer or an amorphous polyamide such as Selar® PA3426 to provide blends having more favorable crystallization rates. However, the such polyamides must be compatible with each other, and/or must efficiently trans-amidate during extrusion. Moreover, the blending of resins prior to extrusion increases the time and expense of the process. Additionally, consistent uniformity of the blend is difficult to achieve, leading to variations in the finished product quality.
Improvements in the foregoing processes are desired.